In An Enquiry Concerning Human Understanding, Humes sets about the task of building a philosophical approach based on aposteriori beliefs. In this, Humes makes claims about the concept of ideas and their origin. However, before one can appreciate the fullness of Humes claims, one must understand where Humes is coming from in his approach to philosophy. The purpose of this essay will be to 1) establish Humes philosophical attitude, 2) define Humes view on the nature of thought and then to consider the claim that the idea of God has its origins in impressions and that no idea can be apriori and finally 3) analyze the response Descartes would have to all of this.

The first step in understanding Humes argument on ideas is to understand what perspective Humes is coming from in writing the Enquiry. The goal of the text, according to Humes, is to conduct a metaphysical investigation of human nature in order to show that human beings are non-rational creatures. For Humes, the human being is not even capable of being motivated to use his reasoning faculties. Add to this Humes belief in empiricism, that is, the view that all knowledge comes from experience, and it becomes clearer still why Humes believes that no idea can be apriori. Humes also uses inductive reasoning in order to prove his argument, Inductive reasoning involves projecting from observed characteristics to unobserved characteristics. In the Enquiry, Humes will use inductive reasoning to bridge the gap between his First Argument Concerning the Origin of Ideas and the very nature of all ideas, including that of the idea of God.

The second step in understanding Humes argument concerning ideas is to understanding how Humes views ideas within the context of the nature of thought. For Humes, all the contents of the mind are termed perceptions. These contents are further subdivided into two major classes, that of impressions and ideas. Impressions are those perceptions which are vivid, intense, and forceful. The feeling of being in the presence of a supremely perfect and infinite being (i.e. God) would be an example of an impression to Humes. On the other end, merely contemplating the power and love of God would be the equivalent of an idea. The concept of the term 'idea' is significant for Humes argument on the idea of God's origin. The idea of God must be treated just as any other idea and thus, be subject to any derived relationships that any other idea would be.

Having established Humes general attitude and primary classifications of thoughts we must now turn our attention to the relationship Humes believes to exist between impressions and ideas. In his First Argument Concerning the Origin of Ideas Humes states "Every idea I've examined is traceable from impressions." In this, Humes examines the contents of his own mind and observes for himself that each and every idea he has had can be shown to have originated from a like impression. Using inductive reasoning this premise leads Humes to conclude that "All ideas are derived from impressions." From the basis of this conclusion (Humes First Thesis), Humes excludes the possibility that any idea can be brought about apriori, and that in fact ideas must be based on aposteriori impressions. This Thesis also includes the idea of God. For Humes, the only way one can contemplate a superior and infinite Being is because that same Being has left a vivid impression of some of His infinite qualities on you.

The next part of this essay shall concern us with Rene Descartes' objections and response to Humes philosophical approaches.

The first objection Descartes would have to Humes philosophical approach would be that of Humes purpose in writing the Enquiry. Descartes goal of Meditations was to build a stable, and lasting, and certain system of knowledge. In that, Descartes implies that the human being is a rational creature capable of discerning knowledge, as opposed to Humes claim that we are basically irrational creatures. Descartes response to Humes claim would be that humans may indeed seem like irrational, unmotivated creatures but that certainly doesn't mean that we're incapable of grasping higher concepts and principles to better ourselves.

Another objection Descartes, would have would concern the role of empiricism in Humes views. Descartes is a rationalist and after he is able to prove the existence of God (and thus, the nonexistence of an Evil Genius) he goes on to reason out the rest of existence. As oppose to Humes who believes that all knowledge is gained aposteriori, Descartes must build his system of knowledge completely apriori because of the possibility that his senses could be deceiving him as revealed in the Dream Argument. Descartes response to Humes insistence on using experience to support his arguments would be that ones senses may not be as reliable as one thinks in supporting a point as evidenced by the shade of color objection to Humes Second Argument Concerning the Origin of Ideas.

The third objection Descartes would have to Humes philosophical approach would lie in Humes use of inductive reasoning. For Descartes, to reason that a few observed events can explain concepts that include all these types of events would be inappropriate and has the potential for running into problems. Deductive reasoning, that of reasoning from general to the specific is the only true way for Descartes to build his philosophy. In the Meditations Descartes uses deductive reasoning to go from God exists (and no Evil Genius exists) to dealing with the Problem of Error and Evil (all errors are avoidable) to the Existence of an External world (no possibility of dreaming). Descartes response to Humes would be that to try to build a philosophy any other way would produce serious gaps leaving significant holes in your arguments.

Descartes final objection would be concerned with the nature Humes relationship between impressions and ideas. Essentially Humes proposes that one mind dependent perception (ideas) must be derived from another mind dependent perception (impressions). For Descartes this is quite illogical, as he states in his Causal Adequacy Principle "The cause of an idea must have at least as high a degree of formal reality as the idea has subjectively." In this, Descartes is saying that mind dependent things (i.e. subjective realty) can only come from mind independent things (i.e. formal reality) of equal or greater value. Descartes response to Humes would be that impressions do not possess enough reality to be the basis of ideas.

In my opinion, Humes argument that ideas are derived from impressions is valid but not sound. In examining my own perceptions I feel that my ideas are derived from something with all the characteristics of an impression but with a greater degree of reality than that which lies inside my mind. In essence, I agree with Descartes Causal Adequacy Principle. If I were to believe Humes argument I would have no cause for believing in an external world or anything "real" (i.e. mind independent). Yet, both my aposteriori and apriori faculties compel me to believe that all my ideas about perceptions must be brought about by something or someone that exceeds the limits of my mind and exists separately of all my perceptions concerning it.

In conclusion, Humes argument that the idea of God has its origin in impressions and that in fact no idea can be apriori is shown through 1) understanding Humes general attitude, 2) Humes concept of perceptions, and 3) Humes First Argument Concerning the Origin of Ideas. Humes treats the idea of God just as any other idea and is thus able to justify his claim. From Descartes perspective though. Humes philosophical approach is unsound. Descartes would object to 1) Humes purpose of the Enquiry, 2) Humes empirical point of view, 3) Humes use of deductive reasoning, and lastly 4) the concept of ides being derived from impressions. For Humes though, the First Thesis is the first step in building a philosophy based on aposteriori beliefs.